Apparatus for winding and unwinding strip material



0 United States Patent l 13,545,694

[72] inventor Kurt Ehrat [56] References Cited A I N gg ig UNITED STATESPATENTS PP 3,275,258 9/1966 Perez 242/755 1 PM P 1968 3,398,914 8/1968Cunningham 242/7543 [45] Patented Dec. 8, 1970 [73] Assignee ClbnLimited Primary Examiner-George F. Mautz Ba el, Switze la dAttorney-Pierce, Scheffler and Parker a company of Switzerland PriorityABSTRACT: Apparatus for winding and unwinding strip [31 1 6107/67material from a spool includes a belt-driven pulley coupled to [54]APPARATUS FOR WINDING AND UNWlNDlNG STRIP MATERIAL 11 Claims, 12 DrawingFigs.

[50] Field of Search 242/672, 67.1, 67.4, 75.5, 75.1, 67.5, 78.6, 78.1,67.3, 75.43, 75.44; 28/35, 36

the spool, two pairs of rollers for driving the belt in one direction orthe other respectively and a brake for stopping the belt. The pairs ofdriving rollers and the brake are controlled in an alternative manner bymeans of a cam arrangement associated with and actuated by aspring-loaded tension lever including a strip tensioning roller aroundwhich the strip material passes on its way to or from the spool. As thetension in the strip material varies, the tensioning lever will move inone direction or the other from an intermediate position in which thecam means applies the brake to the belt. Movement of the tensioninglever in one direction puts one pair of driving rollers into operationthus to drive the belt and pulley in one direction, and movement of thelever in the opposite direction puts the other pair of driving rollersinto operation to drive the belt and pulley in the opposite direction.

PATENTED an". 819m sum 3 OF 7 PATENTED DEC 8 19m SHEET u M 7 PATENTEDDEE 8192B SHEET 7 OF 7 kUrt Ehrafi ,JDRA AQPW WWW APPARATUS FOR WINDINGAND uNwINnINc STRIP MATERIAL This invention relates to apparatus forwinding and unwinding strip material.

In conventional strip winding apparatus the motors driving the windingbobbins or spools are started, stopped, or reversed L by the position ofa lever whose position is governed by the i the tensioning lever.Generally the brake means consist of a band which envelops a brakecylinder and which is tensioned' by a solenoid for generating thebraking force.

Theseknown strip winding devices have certain drawbacks which areprimarily derived from the combination of several strip winding devicesrequiring provision of separate drive motors with associated switchmeans for starting, stopping, and reversing the motor, and so forth foreach winding bobbin or spool and that all the components must bedesigned to handle relatively high loads. This is reflected inrelatively high cost. Load incurred by the starting and stopping of themotors, activating and deactivating the brake solenoids, areconsiderable and interference with neighbouring electronic circuits mayresult. This can be avoided only by providing suppressor devices whichadd to the cost of the apparatus.

The speed of the winding bobbin or spool depends, on the one hand, uponthe speed of the strip and, on the other hand, upon whether the spoolcarries a fully wound roll or an empty roll. The required ratio of therotary speeds of the full and the empty winding spool may be as high as1:4 or even more, in order to keep the speed of the strip perfectlyconstant. The motors must therefore be designed to provide the maximumnecessary speed for the empty spool and also to generate the maximumtorque for rotating the fully wound spool. In other words, the motorsmust be robust. In conventional strip winding apparatus this means thatthe. controlled loads are high and add considerably to the moment ofinertia of the winding spool and the roll of strip material woundthereon.

It is an object, therefore, of the present invention to provide improvedapparatus for winding and unwinding strip material.

In accordance with the present invention, I provide apparatus forwinding and unwinding strip material, comprising a belt-driven pulleyonto and from which the strip material is wound or unwound, at least onetensioning roller over which the strip material is arranged to bepassed, the tensioning roller being mounted on a spring-loadedtensioning lever, a first and second pair of drive rollers, and a brake,the two pairs of drive rollers and the brake being alternativelycontrolled by a cam movable by the tensioning lever so that in a firstposition of the tensioning lever the cam activates the first pair ofdrive rollers to engage the belt to drive it in a first direction, in asecond position of the tensioning lever the brake is actuated by the camto stop movement of the belt and in a third position of the tensioninglever the cam activates the second pair of drive rollers to engage thebelt to drive it in a direction opposite to said first direction, thedrive rollers and brake when engaged with said belt being arranged toprovide a frictional force in excess of that between the belt andpulley.

In apparatus for winding and unwinding a strip material of theafore-described kind, the following preferred embodiments include a beltwhich travels between first and second pairs of continuously drivenrollers and a pair of brakeshoes so alternatively controlled by a camwhich is movable by a tensioning lever that in a first end position ofthe tensioning lever the first pair of drive rollers, in a centreposition of the tensioning lever the pair of brakeshoes and in the otherend position of the tensioning lever the second pair of drive rollers ispressed into contact with the belt and thus activated, the arrangementbeing such that the driving and braking forces between the drive rollersand brakeshoes respectively and the belt exceed the force of frictionbetween the belt and the pulley that is driven by the belt.

In order that the nature of the invention may be more readi lyunderstood, embodiments thereof which are not intended to limit thescope of the invention in any way will be hereinafter more particularlydescribed with reference to the accompanying drawings in which:

FIGS. 1 to 3 are a first embodiment of apparatus according to theinvention shown in three different operating states;

FIG. 4 is a simplified representation of the apparatus in FIGS. 1 to 3illustrating the kinematics of the proposed arrangement;

FIG. 5a is an equivalent diagram of the distribution of forces;

FIG. 5b is a time-speed diagram relating to FIG. 5a;

FIG. 6 is a rewinding apparatus combining two complete systems of thekind illustrated in FIGS. 1 to 3;

FIG. 7 is a modification of the apparatus according to FIGS. 1 to 3adapted to provide three different winding speeds;

FIG. 8 is a simplified section taken on the line VIII- VIII in FIG. 7;

FIG. 9 is a diagram for further elucidating the functioning of theembodiment according to FIGS. 7 and 8; and

FIGS. 10a and 10b represent a modification of a detail in theembodiments according to FIGS. 1 to 3 and 6 to 7.

With reference to FIGS. 1 to 3 there is provided a pulley 4 coupled to awinding bobbin or spool 2 on a shaft 1 for common rotation therewith.The strip material or tape 3 which can be wound on or drawn off thespool 2 runs over rollers 8, 9, l0, and 11. The two rollers 10 and 11are mounted on fixed axles, whereas the two others 8 and 9 are mountedon a tensioning lever 7 which pivots on a fulcrum at 37. An endless belt5 engages the periphery of the pulley 4 and is kept taut by tensioningrollers 12 and 13. These tensioning rollers are each mounted on a belttensioning swivel arm 14 and 15 fulcrumed on fixed pivots l6 and 17. Thetension of the belt is maintained by springs 18 and 19 which apply agiven pull to the swivel arms 14 and 15. The deflection of the belttensioning swivel arms is limited by stops 20 and 21. Cooperating withthat portion of the belt which travels between the two tensioningrollers 12 and 13 are a first pair of forward drive rollers V 22 and 23and a second pair of reverse drive rollers R 24 and 25. Between the twopairs of drive rollers is a brake B comprising brakeshoes 26 and 27. Atleast one roller of each pair of drive rollers 22, 23 and 24, 25 can bedriven by a motor in the direction indicated by arrows. The rollers 22and 24 run in fixed bearings, whereas the two rollers 23 and 25 are eachrotatably mounted on the end of a swivel arm 28 and 29. The swivel arms28 and 29 are fulcrumed on pivots 30 and 31. Springs 32 and 33 urgethe-arms towards the belt 5 and the cooperating fixed rollers 22, 24.The brakeshoe 26 is fixed, whereas the other brakeshoe 27 is mounted ona lever 34 which is deflectable about a pivot at 35. A spring 36 whichis attached to the lever 34 urges the movable brakeshoe 27 towards thefixed brakeshoe 2.6. The pivoted end of the tensioning lever 7 ismodified to form a quadrant 38 which contains a cam slot 39. The trackof this cam slot 39 cooperates with follower elements which in theillustrated embodiment take the form of pins 40, 41, and 42, pins 40 and42 being affixed to the lever arms 28 and 29 of the drive rollers 23 and25 and pin 41 being affixed to the lever arm 34 carrying the brakeshoe27. The pins 40 and 42 are affixed to the ends of their respectivelevers 28 and 29.

The cam slot 39 is so shaped and disposed in relation to the followerelements that only one of the pairs of drive rollers 22, 23 and 24, 25or the brake can take effect at any one time. To this end the cam slotis formed with a recess E for the reception of one of the pins 40, 41,and 42 to activate the element controlled by the pin. The recess Eexceeds the maximum possible deflection of the pins 40, 41, and 42 by anamount d to ensure that the full power of the springs 32, 33, and 36associated with the pins can be exerted to press the respective elementagainst the belt when one of the pins has been received into the recess.The maximum possible deflection of the pins 41 and 42 is determined bythe position of the fixed rollers 22 and 24 and that of the pin 41 bythe position of the fixed brakeshoe 26.

When the tensioning lever 7 is in the upper position shown in FIG. 1 thepin 40 on the lever 28 carrying the roller 23 will be received into therecess. Consequently, the pull of the spring 32 causes the belt to betightly gripped between the two rollers 23 and 22 and to be drivenforward in the direction indicated by arrows on the two rollers.However, when the tensioning lever 7 is in the central position shown inFIG. 2, then the pin 41 associated with the brakeshoe 27 on the swivelarm 34 will be received into the recess E in the cam slot and the pullof the spring 36 will cause the belt to be tightly gripped between thetwo brakeshoes 26 and 27. Finally in the bottom end position of thetensioning lever shown in FIG. 3 the pin 42 will be in the recess E andthe belt will therefore now be gripped between the two rollers 24 and 2Sand driven in the reverse direction indicated by the arrows on theserollers.

In the following description of the manner in which the mechanismillustrated in FIGS. 1 to 3 functions, reference will first be made toFIG. 2 which shows the tensioning lever in its centre position. The beltis therefore gripped between the two brakeshoes 26 and 27 and neitherthe pulley 4 nor the winding spool 2 can move. However, as soon as thestrip material is pulled upwards at PE it will also pull the tensioningarm 7 in the upward direction. The pulley and the winding spool firstremain stationary untilthe tensioning lever has been upwardly deflectedsufficiently for the swivel arm 34 of the brake 26, 27 to have beenretracted by the cam slot 39 in the quadrant 38 and the brake to havebeen released. Further upward deflection of the tensioning lever movesthe recess E far enough for the pin 40 on the swivel arm 28 to bereceived into the recess E. Consequently, the belt 5 will now be grippedbetween the two rollers 22 and 23 and the belt starts to move. Thepulley 4 is engaged by the belt and begins to rotate in the clockwisedirection. The continuously revolving cooperating rollers 22 and 23engage the belt substantially without delay. However, the pulley and thewinding spool which is fixed to the pulley require a short period oftime to run up to speed, during which the belt must slip on the pulley4. The rotation of the winding spool 2 allows the strip to unwind fromthe spool 2. This situation is illustrated in FIG. 1. So long as thespeed of the strip at point PE exceeds the circumferential speed of theroll of strip material on the spool the tensioning lever will continueto be further deflected in the upward direction. When the peripheralspeed of the roll equals the speed at point PE of the strip, thetensioning roller will have reached its maximum angle of deflection, andwhen the peripheral speed of the roll exceeds the speed of the strip atPE the spring 44 will begin to pull the tensioning lever downwardsagain. As soon as the tensioning lever has swung down sufficiently forthe cam slot 39 to withdraw the pin 40 and hence the swivel arm 28 andits roller 23 from contact with the belt and the pin 41 of the swivellever 34 carrying the brakeshoe 27 is received into the recess, the beltwill be practically instantaneously stopped. However, owing to theinertia of the rotating mass the spool 2 will require a given time tocome to rest whilst the belt slips on the pulley. The apparatus willthen be in the position illustrated in FIG. 2. If in the positionaccording to FIG. 2 the strip at point PE is moved downwards, i.e. ifthe normal tension of the strip at point PE is relaxed, then thetensioning lever 7 will descend further until the brake is released andthe drive rollers 24 and 25 grip and drive the belt, causing the belt tobe engaged by the rollers and to be driven in the counterclockwisedirection. This position is illustrated in FIG. 3 and is reached fromthat shown in FIG. 2 in the same way as the latter position is attainedfrom the position in FIG. I. The transition from FIG. 3 back to FIG. 2proceeds in analogous manner. Owing to the relatively large moment ofinertia of the pulley 4, of the winding spool 2, and of the roll 43periods of delay in starting and stopping also occur during thetransitions between the positions shown in FIGS. 2 and 3 and duringthese periods the belt will slip on the pulley.

In order to prevent the strip from being subjected to severe stress thetension at point PE should be as small as possible. The tension at PE isdetermined by the rating of the spring 44 of the tensioning lever and bythe resistance to displacement of the control cam in the quadrant 38, 39of the tensioning lever. This resistance depends upon the efiortrequired for deflecting the swivel arms (28, 29 and 34). This effort isnumerically defined by the distance H of deflection multiplied by thespring force acting on the swivel am. It is therefore desirable tominimise this distance H and the spring force. The distance H may bereduced to as little as a few tenths of a millimetre. The spring force(springs 32, 33 and 36) which determines the gripping power of therollers and brake must be so chosen that the friction between the beltand the drive rollers and the belt and the brakeshoes will definitelyexceed the friction between the belt and the circumference of thepulley. If this were not the case the belt would not slip on the pulleybut it would slip between the drive rollers. Continuous slippage betweenthe drive rollers means excessive wear of the belt. It is thereforedesirable that the friction between the belt and the circumference ofthe pulley should not be very high to permit the gripping force of thedrive rollers to be correspondingly reduced and the tension (at PE) toremain fairly small. On the other hand, the friction between the beltand the pulley should not be less than a given minimum to prevent thetime required for bringing the spool up to speed to become so long that,in the position as shown in FIG. 2 and at an increasing speed of takeoffof the strip at PE when the roll is at its maximum diameter (i.e. itsmoment of inertia is a maximum), the tensioning lever and its rollers 8and 9 would be dragged too far upwards and into contact with the fixedrollers 10 and 11. This would interfere with the proper functioning ofthe mechanism. Conversely the friction between the belt and the pulleymust be sufiicient to ensure that in the most unfavourable circumstancesthe time that elapses before the winding spool and the roll come to restafter having been braked will not exceed the time required by thetensioning lever to move through the entire braking sector whilst thebrake (27) is engaged.

The pulling force of the belt on the circumference of the pulley shouldnot therefore be less than a given minimum value, but at the same timeit should also not be excessive. The pulling force applied by the beltto the pulley should therefore be substantially constant. It is wellknown that in the absence of special arrangements the frictional forces,which are governed by various external factors (contamination, surfacequality, and so forth), are not usually constant. The specialarrangements which in the present instance this embodiment providescomprise a mechanical compensating device which stablises the pull whichthe belt is capable of applying to the circumference of the pulley. Thiscompensating device will now be described by reference to FIG. 4.

FIG. 4 illustrates the proposed system at a time when the pulley isstill stationary and the drive rollers 22 and 23 have just been allowedto move into engagement by the control cam (not shown in FIG. 4, butconstructed as illustrated in FIGS. 1 to 3) for driving the belt in theforward direction (arrow V).

The portion 5A of the belt therefore rides onto the pulley,

whereas the portion 58 rides off the pulley. The endless belt thustravels in the direction of the arrow V. According to a known formulathe relationship between the loads that are transmitted by the portionsof the belt which ride on and off the pulley are defined by where p. isthe coefficient of friction between the belt and the pulley and p is theangle subtended by the arc of contact of the belt with the pulley. Thepull P transmitted by the portion 58 of the belt which rides off thepulley thus always exceeds the pull exerted by the portion 5A of thebelt. Since the forces generated by the two springs 18 and 19 are equaland P, exceeds P the swivel arm 15 will be pulled away from its stop 21(clearance 1), whereas the swivel arm 14 will be pulled into contactwith its stop 20. Consequently the force of spring 18 will cease to haveany effect on the belt; Hence the pull P of the belt will be equal tothe pulling force F, exerted by the spring 19. In other words P P Inview of the practically loss-less deflection of the belt by the roller13 P1= P Pp. It follows that P, P,-, P,-= P eup and P PM eup.

The actual peripheral pull P, applied to the pulley by the belt istherefore represented by the following equation: P, P, P P P eupor P,P,.-(l l/ezp).

It will therefore be understood that, provided the angle p and thecoefficient of friction p. are large, the pull P, applied to theperiphery of the pulley is substantially independent of friction andhence substantially depends only upon the practically constant springforce Pp. For instance, assuming an angle p 180 and a coefficient offriction p.= 0.5, the term e'pp will be about 4.5, l/eup will be about0.22 and hence P, =0.78 P

,If the coefficient of friction were to increase by 100 percent (sayfrom 0.5 to l then eup would become about and Hey. p would be 0.05 sothat P, would be 0.95 PF It will therefore be seen that an increase inthe coefficient of friction by 100 percent raises the effectiveperipheral pull by not more than 20 percent and this fact illustratesthe degree of stabilisation that is'achieved.

Analogous conditions naturally apply when the direction of rotationisreversed or whenthe brake is applied.

Another requirement for achieving an optimum performance of the proposedapparatus is that whenever the belt is suddenly started for forwardrunning, i.e. when the'two-rollers 22 and 23lar e. pressed together bythe spring 32, the friction between the driving rollersand the belt.should remain low to prevent: the belt from getting hot aridfrom beingdamaged or destroyed. The relatively low mass of the belt should be moreor less instantaneously ac'celerated to maximum, speed V,, i.e. theperipheral speed of the drive rollers. Friction due to slippage willthen occur only on the pulley where the specific pressure is low becauseof the large circumference of the pulley and'where cooling is not aproblem; I,

With reference to FIGS. 50 and 5b the further question will now bediscussed how much work A,is expended for accelerating abelt ofm'ass mfrom zero speed to maximum speed V This work is done in the time T(switching time). At the time r== 0 the speed V of the belt is assumedto be zero. When the two rollers 22 and 23 are pressed together theygenerate a force offriction P which accelerates the belt to the maximumspeed V,. When this has been reached the belt continues to travelwithout slip at V,,. During this switching time T the speed is V =7 b t,where b is the acceleration of the. belt, or V =.(P P **t/m;where P isthe force exerted by the rollers 22, 23, P, is the braking force of thepulley and m ,is the equivalent mass of the belt. In this time T'thespeed V, is reached in accordancewith the equation The switching time Tcan therefore be calculated from I f and the work performed is Hence P A=(P Pu-%)-m.V 2

This equation indicates that the force P exerted by the drive rollersshould substantially exceed the braking force P, if the work of frictionis to remain low. If P is, much greater than P,

is the minimum possible work of friction for accelerating the belt. Itwill be seen that this force of friction diminishes in proportion withthe mass m of the belt and that the magnitude of the mass of thewinding-on or drawoff spool including the roll does not enter into theresult. At a speed of V, cm/sec.

for a belt weighing 30 p the work of friction for starting up the cientof friction between the rollers and the belt and, on theother hand, uponthe pressure applied to the belt by the action of the spring 32 (FIG.4). It again transpires that the peripheral pull P, should be asconstant as possible to avoid the need of a spring 32 of unnecessarilyhigh rating, since the spring rating must be overcome by the cam and thetensioning lever and should therefore be as small as possible.

Analogous relationships apply to reverse drive and to the brakingaction.

In FIG. 6 two mechanisms of the kind shown in FIG. 1, (to 3) arecombined to form a single rewinding machine .with asingle driving motorM. In the right-hand system components corresponding to like componentsin FIG. I bear the same reference numerals as in FiG. 1. Like componentsin the lefthand system are likewise identified by the same referencenumerals but they are distinguishedby a prime. Each of the two systemsfunctions independently from the other as has already been describedwith reference to FIGS. 1 to 3. However, for cooperation one system isalways set to wind on and the other to wind off, or both systems arebraked. In the drawing the left-hand system is set to wind on. The stripmaterial travels from point PE to point PE through guide meanswhich areirrelevant to the invention. Treating and/or viewing stations may beprovided between PE and PE. 7

' FIGS. 7 to 9 illustrate an embodiment of the invention speciallydesigned for several different speed ranges. This embodiment istherefore in effect fitted with three pulleys 4,, 4,, and 4 of differentdiameters. As a matter of practice a single pulley structurehaving threestepped diameters is utilized.

They are all mounted on a common rotatable shaft land each' driven by adifferent belt 5,, 5,, and 5,,,. The fixed drive rollers 22 and 24operate to drive all three belts. However, each of the three belts 5,,5,,, and 5,,, is associated with a deflectably movable roller 23,, 23,,,and 23,,, and 25,, 25,,,

25, (25,, ,,,)'and each pair of rollers (23,/25,, 2 11/25 23,,,/25m) isin turn associated with a control cam of its own. 'The three cams areprovided on three quadrants 38,, 38,, and 38 affixed to a common striptensioning lever 7. In principle the arrangement functions in exactlythe same way as that described with reference to FIGS. 1 to 3, exceptingthat the position of the tensioning lever 7 controls three forward andthree reverse speeds. The three control cams are so contrived andrelatively positioned that the system functions as follows: In thehighest position of the tensioning lever 7 the roller 23, is pressedinto contact with the belt and the highest forward speed is thusobtained. If the tensioning lever drops towards its centre position, theroller 23, is withdrawn and the roller 23,,

is pressed against the belt, thereby generating a medium speed. Furtherdownward deflection of the tensioning lever the lowest, the medium andthe highest reverse speeds. The tensioning lever 7 thus functions like agear selector lever. The three cams of the three quadrants 38,, 38 and38 are naturally again so contrived (cf. FIGS. 1 to 5) that only one ofthe rollers or the brake can cooperate with one of the belts at the sametime.

The diagram in FIG. 9in; graph form represents the functional dependenceof the speed of the winding spool upon the position of the tensioninglever.

FIGS. 10a and 10b illustrate a variant of the control cam in which thequadrant 38 formed with a cam track 39 is pivotably mounted and coupledto the tensioning lever 7 by a lost motion mechanism. As illustrated,the control quadrant works on the same shaft as the tensioning lever towhich it is coupled by a sliding pin and slot motion 52-51. The pin 52is fast on the tensioning lever and works in a recess 51 cut into theperiphery of the quadrant. Thisarrangement introduces the lost motioninto the action of the tensioning lever when the latter reverses itsdirection of deflection. The delay S introduced by the lost motion-isdetermined by the length of the recess 51 in the quadrant and thediameter of the pin. When the tensioning lever is deflected upwards(FIG. 10a) the quadrant is engaged as soon as the pin 52 makes contactwith the upper end of the recess 51. However, when the tensioning leveris lowered the quadrant is engaged when the pin 52 is intercepted by thebottom end of the recess 51. This hysteresis effect which is thusintroduced into the working of the control means prevents the tensioninglever from continuously stopping and starting the belt when the leveroscillates within a small angle. After having started the belt thetensioning lever must therefore be deflected through a distance S beforethe belt is again stopped.

The transmission from the drive motor M (H6. 6) to the drive rollers maybe a belt drive, gearing or the like. Either both rollers of a pair oronly thefixed roller may be driven.

lclaim:

1. Apparatus for winding and unwinding strip material comprising a belt,a pulley driven by said belt, a winding spool coupled to said pulley,the strip material being wound onto or drawn off said winding spooldependent upon the direction of rotation of said pulley, first andsecond pairs of driving'rollers between which said belt passes, a brakemechanism for said belt, a spring-loaded tensioning lever, at least onestrip material tensioning roller mounted on said lever and around whichthe strip material passes, and cam means actuated by movement of saidtensioning lever as the tension in said strip material passing aroundsaid tensioning roller varies and operatively connected respectivelywith said first and second pairs of belt-driving rollers and said brakemechanisms for alternative activation dependent upon the position ofsaid tensioning lever, said lever when moved to a first positionactuating said cam means to activate said first pair of rollers toengage and drive said belt and pulley in one direction, said lever whenmoved to a second position actuating said cam means to activate saidsecond pair of rollers to engage and drive said belt and pulley in theopposite direction, and said lever when in a position intermediate saidfirst and second positions actuating said brake mechanism to engage andstop said belt and pulley, said pairs of belt-driving rollers and saidbrake 1 mechanism when engaged with said belt providing frictionalforces in excess of the frictional forces existing between said belt andpulley.

2. Apparatus as defined in claim 1 for winding and unwinding stripmaterial and which further includes a plurality of belt-tensioningpulleys around which said belt passes and which are located intermediatesaid belt-driving rollers and pulley, swivel arms individual to andmounting said belt-tensioning rollers, spring means individual to andbiasing said swivel arms and the belt-tensioning rollers thereon intocontact with said belt so as to tension it, and stop means individual tosaid swivel arms for limiting the movement of said swivel arms in thebelt-tensionin direction.

3. Apparatus as define in claim 1 for winding and unwinding stripmaterial wherein said cam means includes a cam track member actuated bysaid tensioning lever and cam follower means engaged with said track andindividual respectively to said first and second. pairs of belbdrivingrollers and said brake mechanism for actuating the same alternativelyinto engagement with said belt.

4. Apparatus as defined in claim 3 for winding and unwinding stripmaterial wherein said cam track is formed with a recess and said camfollowers are constituted by pins which when engaged with said recessactivate alternatively said pairs of belt-driving rollers and brakemechanism.

5. Apparatus as defined in claim 1 for winding and unwinding stripmaterial wherein each pair of belt-driving rollers includes onepower-drivenroller engaging said belt and rotating on a fixed axis and asecond roller mounted on a spring-loaded swivel arm which normallybiases said second roller into pressing engagement withsaid belt, andsaid cam means includes a cam track member actuated by said tensioninglever and cam followers engaged with said cam track, said cam trackbeing formed with a'recess and said cam followers being mountedrespectively on said swivel arms and serving to shift the correspondingsecond roller in a direction away from said belt except when the camfollower occupies the recess in said cam track.

6. Apparatus as defined .in claim 5 for winding and unwinding stripmaterial wherein said pulley includes a plurality of different drivingsurfaces of different diameters, there being a separate belt correlatedto each different pulley diameter, each said pair of belt-drivingrollers including a common power-driven roller and a plurality of secondrollers each alternatively engageable with a different one of saidbelts, and wherein said cam means when actuated by movement of saidtensioning lever towards said first or second positions from saidintennediate position causes said second rollers to engage said belts insuccession to successively increase the .driving speed of said pulleyand winding spool.

7. Apparatus as defined 'n clai 1 for winding and unwinding stripmaterial wherein said cam means includes a cam I track fonned integrallywith; said tensioning lever and. earn track follower meansoperatively-connected with said first and second pairs of drivingrollers and said brake mechanism.

8. Apparatus as defined in claim 1 for winding and unwinding stripmaterial and which further includes a lost motion mechanism interposedbetween said tensioning lever and said cam means for delaying actuationof said cam means until said v tensioning lever has moved apredetermined distance from its intermediate position.

9. Apparatus as defined in claim 1 for winding and unwinding stripmaterial wherein said cam means includes a pivotally mounted cam memberprovided with a cam track and a plurality of cam track follower meansoperatively connected with said first and second pairs of drivingrollers and said brake mechanism respectively and which further includesa lost motion mechanism interposed between said tensioning lever andsaid cam member for delaying action of said cam means until saidtensioning lever has moved a predetermined distance from itsintermediate position.

V 10. Apparatus as defined in claim 9 for winding and unwinding stripmaterial wherein said lost motion mechanism includes a pin movablebetween two spaced abutrnents, said pin being carried by said tensioninglever and said abutrnents being carried by said pivotally mounted cammember, or vice versa.

11. Apparatus as defined in claim 10 wherein said cam member and saidtensioning lever are mounted for pivotal movement about a common shaft.

